In alloy electroplating, such as gold-tin, on a large panel with multiple smaller boards (e.g., a multi-up circuit board panel or even a large single circuit board), it may be desirable to improve the composition uniformity for eutectic melting point and to increase the productivity by lowering the production costs. Metal and/or metal constituents in the alloy electroplating solution tend to exhibit different deposition rate onto the product. For example, the tin in a gold-tin alloy solution is usually deposited more quickly due to uneven electrical charge across the large panel.
When the alloy is being electrodeposited to facilitate future soldering operations, the melting point of the unevenly deposited alloy will vary from point to point. Any large variation in eutectic melting point of the alloy across the panel will thus create a poor solder joint during later assembly. Often, every part on the panel is un-usable due to the poor quality soldering results achieved when the alloy is deposited in a non-uniform fashion. For other applications, such as nickel-manganese alloy, the mechanical or electrical properties will vary from lot to lot, thus resulting in products with inconsistent performance. Frequently the whole assembly is scrapped after the final testing due to the poor composition uniformity.
For small panels, such as the 6″ or smaller diameter round wafers often fabricated for the semiconductor industry, gold-tin electroplating can often be satisfactorily completed. For larger and/or irregularly shaped panels, uneven deposition due to varying electrical fields becomes a problem. Anecdotally, those of ordinary skill in the art of alloy electroplating have expressed a disbelief that gold-tin electroplating with controlled composition of the deposited alloy is possible, using current commercially available technologies, for panels larger than the 6″ or smaller diameter round wafers currently being alloy-plated.